Singulair's Side Effects
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Printable Side Effect Alert

Adverse reactions to Singulair can occur at any time during treatment with Singulair: Parents have been reporting to Parents United for Pharmaceutical Safety and Accountability that their children began experiencing side effects days, weeks, months, and even years after treatment with Singulair was initiated. Additionally, some parents reported they observed side effects only after a dosage increase. Parents have also reported that side effects worsened, and/or additional side effects manifested after a dosage increase.

An "adverse reaction" is a result of drug therapy that is neither intended nor expected in normal therapeutic use and that causes significant, sometimes life-threatening conditions.

A "side effect" of a drug is any effect that is in addition to its intended effect, especially an effect that is harmful or unpleasant.

These terms are often used interchangeably.

The following list of side effects was compiled from information in the “Adverse Reactions” and “Post-marketing Experience” sections of Singulair's Prescribing Information and Singulair's Patient Information (available at www.singulair.com). This information was checked on August 28, 2009. Although we make every effort to ensure the information on our website is up to date and accurate, we encourage you to review Singulair's Prescribing and Patient Information.

Singulair’s possible side effects include:

weakness (asthenia), fatigue, tiredness, fever, swelling (edema)

increased bleeding tendency, nosebleed (epistaxis), bruising

pharyngitis (sore throat), laryngitis, tonsillitis

Cardiac disorders: Palpitations

Digestive/Gastrointestinal disorders: abdominal pain, stomach pain, stomach or intestinal upset, heartburn, indigestion, belching, bloating, nausea, vomiting, diarrhea, infectious gastroenteritis, pancreatitis; dental pain

Ear problems: otitis (ear infection/inflammation), ear pain

Eye problems: conjunctivitis

Musculoskeletal disorders: joint pain (arthralgia), muscle pain (myalgia) and cramps

Neurological/nervous system disorders: dizziness, headache, drowsiness, paraesthesia (pins and needles sensation)/hypoesthesia (numbness), seizures, convulsions

Psychiatric disorders: agitation including aggressive behavior or hostility, anxiousness, bad/vivid dreams or dream abnormalities, depression,  disorientation (confusion), disturbance in attention, hallucinations, insomnia (trouble sleeping), irritability, memory impairment, restlessness, somnambulism (sleep walking), suicidal thinking and behavior (including suicide), tremor (temper tantrums are listed with "psychiatric disorders" in the CANADIAN "PRODUCT MONOGRAPH" FOR SINGULAIR )

More information about Singulair's psychiatric side effects follows this list.

Respiratory disorders: cough, nasal congestion, sinusitis (inflammation/infection of the sinuses), upper respiratory infection, rhinitis (runny nose), flu, bronchitis, wheezing, pneumonia

Skin and subcutaneous tissue disorders: rash (dermatitis), eczema, urticaria (hives), pruritus (itch), angioedema (swelling beneath the skin), erythema nodosum (disorder of fatty layer under the skin - reddish, painful, tender lumps usually located on the front of the legs below the knees.)

Hepatobiliary disorders: hepatitis, liver-injury

Urinary disorders: pyuria (pus in the urine)

Allergic reactions, including swelling of the face, lips, tongue, and/or throat (which may cause trouble breathing or swallowing), hives and itching

In rare cases, patients with asthma may present with systemic eosinophilia, sometimes presenting with clinical features of vasculitis consistent with Churg-Strauss syndrome, a condition often treated with systemic corticosteroid therapy. These events usually, but not always, have been associated with the reduction of oral corticosteroids. Physicians should be alert to eosinophilia, vasculitic rash, worsening pulmonary symptoms, cardiac complications, and/or neuropathy in their patients. A causal association between SINGULAIR and these conditions has not been established.

You must tell your doctor right away if you get one or more of these symptoms:
-feeling of pins and needles or numbness of arms or legs
-flu-like illness 
-severe inflammation (pain and swelling) of the sinuses (sinusitis)



ASTHMA was reported as a "drug related adverse experience" in children ages 6 months to 2 years of age in a clinical study of 175 pediatric patients. Canadian "Product Monograph" for Singulair and Singulair 4 mg granules “Local Prescribing Information” for healthcare professionals in UAE, Bahrain, Kuwait and Qatar – text revised December 2003


According to the Canadian "Product Monograph" for Singulair, in a clinical study of 175 pediatric patients 6 months to 2 years of age, HYPERKINESIA was reported as a drug related adverse experience in >1% of patients treated with SINGULAIR and at a greater incidence than in patients treated with placebo. We could not find this information in the "Adverse Reactions" section of Singulair's US label (6/20/09).

Singulair 4 mg granules “Local Prescribing Information” for healthcare professionals in UAE, Bahrain, Kuwait and Qatar – text revised December 2003 Also lists HYPERKINESIA as a drug related adverse experience in >1% of patients treated with SINGULAIR and at a greater incidence than in patients treated with placebo in a clinical study of 175 pediatric patients 6 months to 2 years of age. We could not find this information in the "Adverse Reactions" section of Singulair's US label (6/20/09).


Hyperkinesia is a movement disorder characterized by excessive spontaneous movement or abnormal involuntary movement.

The following are classified as HYPERKINETIC DISORDERS:

tremor, tics, myoclonus, hemiballismus, dystonias, chorea, athetosis


In the US National Library of Medicine/US National Institutes of Health MedlinePlus Medical Dictionary, a search for HYPERKINESIA yields HYPERKINESIS which is defined as:

1: abnormally increased and sometimes uncontrollable activity or muscular movements: hyperactivity

2: a condition especially of childhood characterized by hyperactivity

HYPERACTIVITY is defined as "a state or condition of being excessively or pathologically active; especially: ATTENTION DEFICIT DISORDER.

Singulair's Product Monograph and Local Prescribing Information referenced above do not specify the type of hyperkinesia reported in the study.

According to Public Citizen's WorstPills.org website, which lists SINGULAIR as a Do Not Use drug, SINGULAIR can cause blood vessel inflammation, liver disease, lupus, and recurrences of ulcerative colitis. Follow this link for more information: http://worstpills.org/results.cfm?drug_id=1026&x=17&y=4

Among the side effects/adverse reactions listed on Singulair's label are "psychiatric disorders." Because psychiatric disorders can be disabling and more than 90% of all suicides are related to a mood disorder or other psychiatric illness*, it is essential for parents to have a complete understanding of, and be able to recognize, the symptoms of the psychiatric disorders associated with Singulair.

When observing your child's behavior, look for patterns of behavior. For example, do not panic if your child occasionally has a temper tantrum when you tell him to turn off the television. However, if after beginning treatment with Singulair, your child begins having uncharacteristic, violent, or age inappropriate temper tantrums on a daily basis over minor and petty issues, he or she might be showing signs of an adverse reaction.

A special note to parents whose children have been on Singulair for most of their lives: the behaviors and mood you have come to accept as your child's personality may actually be the manifestations of an adverse reaction to Singulair.


An unpleasant state of extreme arousal, increased tension (anxiety, stress, jitters), and irritability. Extreme agitation can lead to confusion, hostility, and hyperactivity.*

Child may have difficulty concentrating or making decisions, be easily distracted, have difficulty sitting still or controlling impulses, and may engage in aggressive behavior.

Example: Child may have difficulty participating in quiet activities (such as reading); may fidget, move constantly, or wander; may talk too much, antagonize peers or instigate fights.

The inattentiveness, over-activity, and poor impulse control of children experiencing an adverse reaction to Singulair have been erroneously attributed to Attention Deficit Hyperactivity Disorder.****


Aggression is described as hostile (antagoinnistic, unfriendly, hateful) or destructive behavior or actions** and can involve:

- unprovoked violent action 
- deliberately unfriendly behavior
- physical or verbal behavior that is intended to cause pain or harm to another.

Example: Child may be oppositional, defiant, combative, quarrelsome; may threaten harm to others; may engage in purposeful and unprovoked attacks on others.


Anxiety is a feeling of apprehension or fear.

Anxiety is often accompanied by physical symptoms, including:
twitching, trembling or tremor; muscle tension; headaches; sweating; dry mouth; difficulty swallowing; abdominal pain (may be the only symptom, especially in a child)

Sometimes other symptoms accompany anxiety:
dizziness; rapid or irregular heart rate; rapid breathing; diarrhea or frequent need to urinate; fatigue; irritability, including loss of temper; sleeping difficulties and nightmares; decreased concentration; sexual problems (in adults) *

Children may express anxiety in the following ways:

-excessive worry (child shows age inappropriate separation anxiety, child worries constantly that parents are going to die)

-abnormal fear of leaving the home (child predictably shows resistance or throws tantrums whenever it is time to go somewhere)

-obsessive compulsive behavior: persistent, irrational, uncontrollable thoughts/behaviors (constantly talking about a particular subject to the extent that it interferes with normal communication, worrying about germs, repeated hand washing or checking things)

-phobias: irrational and disruptive fears of specific objects or social situations


In addition to nightmares, parents have reported night terrors: a sleep disorder in which a person quickly awakens from sleep in a terrified state.

Also called pavor nocturnus or sleep terrors, they occur during deep sleep and usually happen in the first half of the night. The child often screams, and will usually not remember the details of the scare. You may be unable to talk to a child who is having a night terror. In contrast, nightmares are normal on occasion, especially after someone watches frightening movies/TV shows or has an emotional experience. A person may remember the details of a dream upon awakening, and will not be disoriented after the episode.*

In research conducted by Rebecca Bernert, a doctoral candidate in clinical psychology at Florida State University who specializes in the relationship between sleep and suicidal thoughts and behaviors, the presence of severe and frequent nightmares or insomnia was a strong predictor of suicidal thoughts and behaviors.
Other studies have established a link between chronic sleep disruption and suicide.

Sleep complaints, which include nightmares, insomnia and other sleep disturbances, are listed in the current Substance Abuse and Mental Health Services Administration's inventory of suicide-prevention warning signs.

For more information read Wish Fulfillment? No. But Dreams Do Have Meaning


In Singulair's clinical trials, depression was reported in children taking Singulair (montelukast) and in adults taking Singulair (montelukast) and placebo. In one adult in the montelukast group, depression was considered drug related by the investigator.

FDA Medical Review for Singulair 5 MG (page 21)
FDA Medical Review for Singulair 10 MG (pages 78-80)

Depression may be described as feeling sad, blue, unhappy, miserable, or down in the dumps. Most of us feel this way at one time or another for short periods.

Clinical depression is a mood disorder in which feelings of sadness, loss, anger, or frustration interfere with everyday life for an extended period of time. Symptoms include:

-trouble sleeping or excessive sleeping
-dramatic change in appetite, often with weight gain or loss
-fatigue and lack of energy
-feelings of worthlessness, self-hate, and inappropriate guilt (low self esteem)
-extreme difficulty concentrating
-agitation, restlessness, and irritability (and sudden bursts of anger)
-inactivity and withdrawal from usual activities
-feelings of hopelessness and helplessness
-recurring thoughts of death or suicide

Depressed children may not have the classic symptoms of adult depression. Watch especially for changes in school performance, sleep, and behavior.*

Mood disorders are characterized by inappropriate, exaggerated, or limited range of feelings. To be diagnosed with a mood disorder, feelings must be to the extreme.  In other words, crying, and/or feeling depressed, suicidal frequently. Or, the opposite extreme, having excessive energy where sleep is not needed for days at a time and during this time the decision making process is significantly hindered. Bipolar disorder (which has also been reported as an adverse reaction to Singulair) is also a mood disorder.***

The Substance Abuse and Mental Health Services Administration, CDC, NIH, HRSA, and IHS recognize depression as a risk factor for suicide. It is estimated that about 60% of people who commit suicide have had a mood disorder (e.g., major depression, bipolar disorder, dysthymia).




Hallucinations involve sensing (seeing, hearing, feeling, smelling, or tasting) things that aren't there while a person is awake and conscious.*****


Seeing patterns, lights, beings, or objects that aren't there
Hearing voices when no one has spoken
Feeling a crawling sensation on the skin


Insomnia is defined by the National Institutes of Health* as:
"a hard time falling or staying asleep."

According to the FDA's Updated Information on Leukotriene Inhibitors: Montelukast (marketed as Singulair), Zafirlukast (marketed as Accolate), and Zileuton (marketed as Zyflo and Zyflo CR), in clinical trials, sleep disorders  (primarily insomnia) were reported more frequently with all three products compared to placebo.

We could not find sleep disorders and insomnia listed on Singulair's label as side effects reported in clinical trials (6/20/09).

In research conducted by Rebecca Bernert, a doctoral candidate in clinical psychology at Florida State University who specializes in the relationship between sleep and suicidal thoughts and behaviors, the presence of severe and frequent nightmares or insomnia was a strong predictor of suicidal thoughts and behaviors.
Other studies have established a link between chronic sleep disruption and suicide. 

Sleep complaints, which include nightmares, insomnia and other sleep disturbances, are listed in the current Substance Abuse and Mental Health Services Administration's inventory of suicide-prevention warning signs.

For more information read Wish Fulfillment? No. But Dreams Do Have Meaning


The state of being easily irritated or annoyed; readily excited to impatience or anger; abnormally sensitive to a stimulus. Younger children may be fussy or whiny; older children may get extremely angry over imagined slights or minor disagreements/issues; child may be oversensitive to or intolerant of loud noises, bright lights, or physical sensations. 

A parent reported that a medical professional recommended her child be evaluated for Asperger syndrome (an autistic spectrum disorder) when she reported that her child was hypersensitive to tags in his clothes, seams in his socks, and his clothes and shoes always felt "too tight". This behavior stopped after the child stopped taking Singulair. Other children experiencing adverse reactions to Singulair were suspected of being Autistic..****


Another term for agitation.


Somnambulism (sleepwalking) is a sleep disorder that falls under the parasomnia group. Parasomnias are undesirable motor, verbal, or experiential events that occur during sleep. Night terrors/sleep terrors are also in this group.***


Suicide is the act of deliberately taking one's own life. Suicidal behavior is any deliberate action with potentially life-threatening consequences, such as taking a drug overdose or deliberately crashing a car. Suicidal behaviors can accompany many emotional disturbances, including depression...More than 90% of all suicides are related to a mood disorder or other psychiatric illness.*

Early signs:

statements or expressions of guilt
tension or anxiety

Critical signs:

sudden change in behavior, especially calmness after a period of anxiety
giving away belongings/attempts to "get one's affairs in order"
direct or indirect threats to commit suicide
direct attempts to commit suicide

Suicide attempts and threats should always be taken seriously. About one-third of people who attempt suicide will repeat the attempt within 1 year, and about 10% of those who threaten or attempt suicide eventually do kill themselves.*


Involuntary (not on purpose) shaking of the body or limbs. 

Tremors may affect the hands, arms, head, eyelids, voice box, or other muscles. They rarely affect the legs or feet.

The shaking usually involves small, rapid movements -- more than 5 times a second.

The tremors may: occur when you move (action-related tremor), and may be less noticeable with rest; come and go; disappear with sleep; get worse with stress, caffeine, and certain medications; not affect both sides of the body the same way.

Head nodding may be a symptom of a tremor.

If the tremor affects the voice box, the voice may have a shaking or quivering sound.*

EOSINOPHILIA is an increased number of eosinophils. Eosinophils are a type of white blood cell, which contain particles filled with chemicals that fight off infections and are one of the types of cells involved in allergic reactions. Eosinophils are found in small numbers in the blood and small intestine. The body may produce more of them in response to allergic disorders, inflammation of the skin, and parasitic infections. If eosinophils move outside the bloodstream/intestines into organs and tissues, they can cause inflammation and damage.*****

For example, if eosinophils invade the esophagus, the following symptoms may occur: nausea, regurgitation, vomiting, abdominal pain, a burning feeling similar to acid reflux (heartburn) that does not respond to antacids, difficulty swallowing and gagging, feeling like something is stuck in the throat. Children may be reluctant to eat and develop irrational aversions to certain foods.

VASCULITIS is an inflammation of the blood vessels. In vasculitis, the body’s immune system mistakenly attacks the body’s own blood vessels, causing inflammation that can damage the blood vessels and lead to a number of serious complications.

Vasculitis is sometimes a side effect of the body's response to an infection or an allergic reaction to a medication. 

Symptoms may include include general aches, pains, and sickness, such as fever, loss of appetite, weight loss, fatigue (feeling tired) and weakness.

Other symptoms may be specific to certain body systems or organs:

Skin: a variety of skin changes, including purple or red spots. The changes may look like clusters of small dots, splotches, bruises, or hives. They may be itchy or painless.
Joints: aches and arthritis if the joints are affected.

Lungs: may experience shortness of breath or even cough up blood. On a chest x-ray, lung symptoms may look like pneumonia, even though they are not.

Gastrointestinal tract: may include ulcers in the mouth, abdominal pain or bloody diarrhea

Sinuses, nose, and ears: sinus infections, chronic middle ear infections, ulcers in the nose, hearing loss.

Eyes: blurring or loss of vision.

Brain: headaches, confusion, changes in behavior, or strokes.

Nerves: numbness, tingling, and weakness in various parts of the body; loss of feeling or strength in the hands and feet or shooting pains in the arms and legs.*****

CHURG-STRAUSS SYNDROME is a type of vasculitis. It can affect many different organs, but it most commonly affects the lungs, skin, kidneys, and heart. Many people who are diagnosed with Churg-Strauss syndrome also have asthma. They may have had preexisting, newly diagnosed, or recently worsened asthma when diagnosed with Churg-Strauss syndrome.******

Churg-Strauss Syndrome is also called Allergic granulomatosis angiitis.

CSS can also involve the central nervous system, peripheral nervous system, gastrointestinal system, musculoskeletal system, and the optic nerve.

Refer to the "Links and Resources" page for more information.



ASTHMA symptoms in children with no history of asthma who were prescribed Singulair for allergies

Resolution of asthma symptoms when Singulair was discontinued

bed wetting (enuresis)

daytime wetting accidents

daytime soiling accidents (encopresis)

frequent urination

unpredictable outbursts

vocal and motor tics (blinking, throat clearing, mouth opening/closing, sniffing)

head drops (seizure disorder)

Erythema Multiforme (allergic rash believed to involve damage to blood vessels of skin)

cold sores

hair loss

bleeding ears

difficulty swallowing/lump in throat

sensation of choking

fear of eating/choking

damage to nerves in the eye

swollen optic nerves due to intercranial hypertension

opthalmic migraine with persistent visual deficits

bipolar disorder

depression requiring hospitalization

trichotillomania (pulling out one's own scalp or body hair)


severe nail biting

bruxism (teeth grinding)

excessive sweating

excessive thirst

excessive hunger

appetite loss

weight gain

weight loss


dilated pupils

intestinal ulcers

stomach ulcers


If your child experienced symptoms, behaviors, or other medical conditions while taking Singulair that are NOT on Singulair's label, please contact us and indicate what they were and if they resolved when treatment with Singulair was stopped.

Singulair Adverse Events reported to FDA in 2008 (patientsville.com) 

The United Kingdom's Medicines and Healthcare Products Regulatory Agency publishes post-marketing medication adverse reactions on their website. View their "Drug Analysis Prints" HERE. Reports for Singulair are listed under "montelukast."

The United States Food and Drug Administration publishes data from he Adverse Event Reporting System (AERS) HERE. The files listed on this page contain raw data extracted from the AERS database for the indicated time ranges and are not cumulative. The files, which are available in ASCII or SGML formats, include:demographic and administrative information and the initial report image ID number (if available); drug information from the case reports; reaction information from the reports; patient outcome information from the reports; information on the source of the reports; a "README" file containing a description of the files.

Parents report that children begin to exhibit a remission in both the intensity and frequency of symptoms shortly after they stop taking Singulair, sometimes within days. To our knowledge, recovery from symptoms that manifested during treatment with Singulair has not been studied. At this time, there is insufficient evidence to prove or disprove permanent damage. To read or submit recovery stories, CLICK HERE.

Some over the counter medicines also have psychiatric or behavioral side effects, which may not be listed on product packaging or product websites. 

One source of information is WebMD Drugs & Medications A-Z. Click on the "Does [name of drug] have any side effects?" box after clicking on the "Side Effects" tab.

Read: Fall Allergy OTC Medicines - Speak With Your Pharmacist

FDA MedWatch Adverse Event Reporting System, 

*MedLine Plus Medical Encyclopedia, a service of the US National Library of Medicine and the National Institutes of Health

**The American Heritage® Dictionary of the English Language, Fourth Edition. Retrieved September 24, 2008, from Dictionary.com

***Diagnostic and Statistical Manual of Mental Disorders Fourth Edition, presented by
AllPsych ONLINE, one of the largest and most comprehensive psychology websites on the Internet. The DSM-IV is published by the American Psychiatric Association and covers all mental health disorders for both children and adults. It is the standard classification of mental disorders used by mental health professionals in the United States.

****This information is based on parent reports submitted to or reviewed by Parents United for Pharmaceutical Safety and Accountability advocates.

*****From MedlinePlus, a service of the US National Library of Medicine and the National Institutes of Health:

******From the National Heart Blood and Lung Institute website:


Disclaimer: Parents United for Pharmaceutical Safety and Accountability is a volunteer patient advocacy group. Consult a licensed health care professional before making any medical decisions. Do not stop administering an asthmatic child's medications without the supervision of the child's healthcare provider. The information on this site is intended for educational purposes and should not be construed as medical advice. It is accurate to the best of our knowledge. If you discover an inconsistency, please bring it to our attention.